Negative resistance devices are used in the field of application of electromagnetic wave oscillators in combination with a resonator. It is known that such an oscillator generates an electromagnetic wave including at least part of the frequency region from the millimeter wave band to the terahertz wave band (not less than 30 GHz and not more than 30 THz) (to be also referred simply as terahertz wave). Non Patent Literature 1 discloses an oscillator formed by monolithically employing a negative resistance device on a substrate. In the disclosed oscillator, a slot antenna is integrally formed on a semiconductor substrate that carries a negative resistance device and a resonator structure and a gain medium are monolithically arranged.
FIG. 8 illustrates the oscillator disclosed in Non Patent Literature 1. In the oscillator, a resonant tunneling diode (S-RTD 11) having a Schottky barrier is employed as negative resistance device at the collector side. A slot antenna is employed as resonator. The slot antenna of Non Patent Literature 1 is formed as a metal pattern 12 on the semiconductor substrate and capacitors 13, 14 are arranged at the ends of the slot. The oscillator of Non Patent Literature 1 also has a rectifier diode 15. The rectifier diode 15 operates as stabilizing circuit for suppressing parasitic oscillations. A parasitic oscillation specifically refers to a oscillation generated parasitically in a frequency band different from an intended frequency and located at the low frequency side. Such a parasitic oscillation can give rise to problems in oscillators employing a negative resistance device in that it remarkably lower the oscillation output at an intended frequency. So, provision of a stabilizing circuit is very important in an oscillator employing a negative resistance device. For details, refer to Non Patent Literature 2. According to the literature, the impedance of the power supply for supplying a bias in a frequency region not lower than DC and lower than ωosc needs to be low in order to suppress parasitic oscillations, provided that the oscillation wavelength and the oscillation frequency of an oscillator are λosc and ωosc respectively. As a technique for achieving this purpose, a low impedance circuit (e.g., a shunt rectifier diode) should be arranged at a position within λosc/4 as viewed from the S-RTD toward the power supply side. For this reason, in FIG. 8, a rectifier diode 15 is integrally arranged at a position within λosc/4 as viewed from the S-RTD 11 toward the side of the power supply 16. In FIG. 8, 17 represents the sum of the internal resistance of the power supply 16 and the resistance of the connection line.
Citation List
Non Patent Literature
NPL 1: Journal of IEEE ELECTRON DEVICE LETTERS, Vol. 18, 218 (1997)
NPL 2: Journal of IEEE MICROWAVE AND GUIDED WAVE LETTERS, Vol. 5, 219 (1995)